The present invention relates to a radiation detecting apparatus using a scintillator which emits light when the radiation such as X rays, .gamma. rays, or the like when radiated, and, more particularly, to a radiation detecting apparatus for an X-ray computerized tomography scanner (hereinafter, referred to as an X-ray CT).
In a radiation examining apparatus such as an X-ray CT, it is necessary to provide a radiation detector having high sensitivity since in, for example the medical field it is imperative to minimize exposure of patients to X rays the radiation detector with a relatively large S/N ratio. In the X-ray CT, X rays, a strength of which is changed by passing through the body to be examined, are simultaneously detected by a plurality of radiation detectors. In such a case, even if the energy strength of X rays changes over a wide range, it is necessary for each detector to represent substantially the same characteristic as other detectors against X rays. In other words, it is necessary to match the characteristics of each detector.
A radiation detector of the aforementioned type has been proposed which comprises a combination of a scintillator for transforming the energy of radiation into the visible light or near ultraviolet radiation, near infrared radiation, and a photoelectric device for converting the light radiated from the scintillator into an electric signal.
In, for example, U.S. Pat. No. 4,317,037, a detector is proposed which includes a combination of a scintillator consisting of the particles of scintillator material and a silicon photodiode. While the characteristics of the individual scintillator material particules may slightly differ, they are sufficiently mixed and used as single scintillator, so as to reduce a variation of the characteristics as a scintillator. In the proposed arrangement the light radiated from inside of the scintillator can be easily directed or supplied toward the outside by including the scintillator or distributing the scintillator into one or more layers.
In commonly assigned U.S. application Ser. No. 313,171, a radiation detector using powder scintillator is proposed for further improving the S/N ratio.
A radiation detecting apparatus employed in a radiation examining apparatus such as an X-ray CT is constructed in such a manner that a number of the aforementioned type of radiation detectors are arranged through a radiation shielding plate using a thin plate of, for example W, Ta, Mo, or the like each of which exhibit a high radiation absorbing property.
Conventional photoelectric devices may take the form of, for example, a photomultiplier tube, microchannel plate photodetectors, semiconductor photosensitive device (Si photodiode, etc.), or the like. For increasing an effectiveness of the radiation detector for the X-ray CT of the high density and multielement type, a small semiconductor photosensitive device is generally employed so as to permit the construction of a high density photodetector.
To enable a partitioning between each of the adjacent (small radiation detectors) in the high density scintillation radiation detector and multielement type a combination of the scintillator and photoelectric device is employed.
An object of the present invention resides in providing a radiation detector which effectively uses the incoming radiation, has an excellent productivity, and is reliable when installed and used in the radiation detecting apparatus, thereby eliminating the drawbacks in production, performance and structure in the prior-art radiation detector.
To accomplish the above object, in accordance with the present invention, a plurality of radiation detectors each consisting of a scintillator and a photosensitive detector divided by radiation shielding plates, with a cushioning material being employed to make a light reflecting sheet come into close contact with the radiation shielding plates for optically isolating each of the adjacent radiation detectors.